ellipsis:
In grammar, the omission of a word or words neccasary for complete construction but understood in context. Usually represented with "..."

Example:
"After all the lone trail is the best... I'll never stop wandering."
-Jon Krakauer, passage from dairy entry of Christopher McCandless


Explanation:
The purpose of ellipsis here is simple. Krakauer want to get his point across quickly and swiftly. He doesn't want pointless information to distract the reader from the main point, that McCandless likes the lone trail, and wants to continue on it. The ellipsis shortens the passage, making it easier for the reader to understand and get the purpose.